PTL 1 discloses the following technical idea as a method for communication between a camera that serves as an image pickup apparatus, and an interchangeable lens attachable to the camera. PTL 1 discloses a technique that performs synchronous serial communication at a first transmission rate, at which even an old-type interchangeable lens can make communication, and if the attached interchangeable lens is judged as a new lens with regard to the content of the communication, the communication is changed to synchronous serial communication at a second transmission rate that is higher than the first transmission rate. PTL 1 also describes that a circuit for a communication terminal is changed from open-drain type to CMOS type that is suitable for high-speed communication when the transmission rate is changed. This technique can provide a configuration that can operate in combination with an old-type interchangeable lens although the transmission rate is low, and that can operate in combination with a new-type interchangeable lens at a transmission rate that is increased by a certain level.